It takes two, baby

Hybrid laser welding processes make strides in manufacturing

Hybrid laser-arc welding has been around for a while, but only recently has it gained steam, with more industries turning to the technology for a faster way to make components lighter with less heat input and minimal distortion while still maintaining part tolerance.

Hybrid laser-arc welding (HLAW) is not a new concept, but it has gained in popularity recently. Faster travel speeds, less heat input and distortion, and higher tolerances make HLAW a great alternative to laser welding or arc welding processes alone.

The most common combination is laser and gas metal arc welding (GMAW), but the laser also can be paired with gas tungsten arc welding (GTAW) or plasma arc welding (PAW). When combined, the technologies work synergistically by maximizing the laser's ability to provide deep-penetrating welds quickly while capitalizing on attributes of GMAW, GTAW, and PAW such as gap tolerance and joint fit-up.

Craig Bratt, laser division manager of the Fraunhofer Center for Coatings and Laser Applications, Plymouth, Mich., has 15 years' experience working with lasers. His firm, along with Michigan State University, East Lansing, Mich., is dedicated to R&D initiatives; new product and process development; application development; and design and integration of pilot production systems in areas such as advanced hybrid laser welding, laser cutting, laser remote welding, and surface treatment technologies such as laser cladding and hardening.

Most of Fraunhofer's R&D has centered on industrial clients who are looking to make the jump from conventional welding processes to advanced laser processes, such as HLAW.

"They want to know what laser hybrid will give them, how much faster they'll be able to go, how much more consistent the weld quality will be, and how much less heat they'll put in to the surrounding material. Often they'll give us some test material or prototype components and ask us to show them what the results would be using hybrid versus what they are using right now,"Bratt said.

In a recent interview with Practical Welding Today, Bratt explained in further detail why HLAW is becoming more and more attractive for industrial applications and how adopters of the technology can ensure successful implementation of the process.

PWT: What are the advantages of combining laser with GMAW, GTAW, or PAW?

Bratt: One of the main advantages of the laser process is that because of its high energy density, deep and narrow welds can be produced at higher speeds than those normally associated with arc welding processes. The downside to the laser process is that it requires extremely precise fit-up between the parts to be welded to achieve consistent weld quality.

On the other hand, arc welding processes, particularly GMAW, have the ability to bridge relatively wide fit-up gaps between the parts being welded. The downside to conventional arc welding processes is their travel speeds, which typically are slower than the laser process, with much wider fusion zones and higher heat input and distortion in the surrounding material.

When the laser beam process is combined with an arc from, for example, GMAW, the travel speeds achieved can be equal to or faster than those associated with the laser process alone. As an added benefit, GMAW helps compensate for part fit-up variation, which allows the laser to be introduced into applications that would otherwise not be possible.

The laser acts as a stabilizer for the arc, which helps to root the arc to the weld joint of the material being welded, resulting in improved weld bead consistency due to the increased arc stability.

PWT: Which materials are best-suited for HLAW?

Bratt: Any material you can weld with a conventional laser or arc process can be welded using hybrid technology. So far most applications have focused on steel and aluminum, where reduced distortion, increased welding speeds, and improved weld quality are some of the benefits that have been reported. We have worked on successful development programs for applications with steel, aluminum, copper, and titanium to date.

PWT: How do you determine which HLAW process to use?

Bratt: This is mainly governed by material thickness and, to some degree, the requirements of the individual application. In general, laser/GTAW and laser/PAW tend to be used for thinner sheet metal applications. Laser/GMAW generally is reserved for welding thicker sections, although it has been used on automotive sheet metal applications as well.

PWT: In what applications is hybrid welding most beneficial?

Bratt: The automotive and shipbuilding industries were among the first to adopt this technology. However, many others have followed suit or are currently evaluating the process, such as the aerospace and nuclear energy sectors.

In the shipbuilding industry, the laser/GMAW process has facilitated a significant reduction in weld distortion and associated rework compared to the previous arc welding processes used. Likewise, automotive applications have used both laser/GMAW and laser/PAW for body assembly welding, particularly for aluminum sheet metal components.

PWT: What is an ideal candidate for HLAW?

Bratt: Any component or assembly that requires high weld quality, increased welding speeds, and minimal heat input and distortion but might not be readily adaptable to the conventional laser welding process, particularly where part fit-up is an issue.

If you can get your components to fit together tightly enough for laser welding alone then you should go ahead and [use laser welding by itself]. But in certain applications, manufacturers just aren't able to do that. That's when you need to pair it with [GMAW, GTAW, or PAW] to improve the tolerance of the process and to close those gaps.

PWT: What is the most important factor in ensuring success with HLAW?

Bratt: Design for manufacture really is the key to successful implementation of hybrid laser-arc welding. Joint access, joint configuration, and part tolerances all play a part in improving the chances for success.

The process will benefit you more if you design the joint in such a way that you know you have the right access, the right approach to the joint, and the best possible fit-up. That makes a huge difference. All too often manufacturers have component designs that have been around for 10 or 20 years and they try and throw a whole new process at it, and that doesn't necessarily work. That's not the fault of the process; that's the fault of the component, which was designed for something totally different. n

Amanda Carlson

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